Process for the oxidation of white mineral oils to dicarboxylic naphthenic acids



2,725,396 Patented Nov. 29, 1955 PROCESS FQR THE OXIDATION OF WHITE MIN- ERALS OILS TO DICARBOXYLIC NAPHTHENIC ACID Joseph Winkler, Queens, N. Y., assignor to American Collo Corporation, New York, N. Y.

N Drawing. Application March 30, 1954, Serial No. 419,900

3 Claims. (Cl. 260514) White mineral oils are considered intermolecular mixtures of naphthene rings with paraffin side chains. They are practically free of aromatic and naphthene parafiin side chain compounds and solid paraffin waxes. White mineral oils are compounds which have the following basic structure:

I CH1 CHa Depending on its molecular weight, n is in the range of 5 to 40. In orderto make a white mineral oil, the mineral oil distillate, produced from crude oil, must be properly purified. This purification is done normally by ex haustive treatment with sulphuric acid monohydrate and later with large amounts, in two to washes, with oleum, containing 20% and more of free S03. In order to remove from the sour oil the sulphonated products, this oil is again treated in the last wash with sulphuric acid monohydrate. In the final treatment, the sour white mineral oil is deacidified with alcoholic solutions of caustic soda and absorbent clay in order to obtain an entirely acid-free, water-free white mineral oil.

It is known that white mineral oils can be oxidized with air, with or without catalysts, under atmospheric pressure or at pressures up to 50 atmospheres; at temperatures ranging from 100 to 200 C., to monocarboxylic acid products. These products, however, are dark colored and malodorous and their sodium salts cannot be separated by salting out. Lighter monocarboxylic acid products are obtained by partial oxidation of white mineral oils, when only a part of the oil is converted by oxidation to corresponding monocarboxylic acids having the following basic structure:

II CH: CH:

om writ M00011 The unchanged, non oxidized main part of the white oil, after separation from the produced acids (11), by conventional methods of selective extraction, is returned back to the oxidation process. The produced monocarboxylic acids are utilized for the production of industrial soaps, soap based greases, etc. However, because of the low quality of these acids (dark color, sharp odor), the air oxidation of white mineral oils to monoearboxylic acids was used industrially only during World War II, in Ger many, and later abandoned when fatty acids again became abundant.

, The object of this invention, is to provide a process for the manufacturing of dicarboxylic naphthenic acids from white mineral oils by a new two-step liquid phase oxidation, which comprises:

Step N0. 1.Exhaustive air oxidation Exhaustive oxidation of white mineral oils with air under pressure at temperatures of from 100 to 200 C., in the presence of a catalyst. As an intermediate product there is obtained a mixture of a small amount of unchanged white mineral oil (I) with more than of the following monocarboxylic acids: (II) naphthenic acids; (III) hydroxy-naphthenic acids; (IV) carbonyl-naphthenic acids; and their innerand hetero-esters (V, VI, and VII). 7

III CH3 CHzOH CHa ICHE/MCOOH IV CH: COH

CHa- -'/CH:IMCOOH V CH3 CHzO f3 CH3 --/CH2/mCO VI CH1 CHzO-OC/CHz/m CH;

CH; /C.Hz/,,COOH CH3 CH3 VII 7 CH: CHzOOC/CHz/m CH;

CEQICHZIMCOOH Cfia COH Step No. 2.-Exhaustive oxidation with an aqueous solution of a peroxide salt The product from the exhaustive air oxidationas described above, is a two-phase, malodorous, dark brown, highly viscous oil. This intermediate material, is according to the present invention further exhaustively oxidized with an aqueous concentrated solution of a peroxide salt, at temperatures not higher than C. I have found that any peroxide salt which is soluble in water performs in the same manner and gives the same desired result; i. e.

the formation of dicarboxylic naphthenic acids. Such cheap VIII 0H3 COOH on, 4 om .,.oooH

Depending in its molecular weight, m is in the range of 0 to 25. This mixture of homologous dicarboxylic naphthenic acids contains, besides small amounts of unchanged white oil (I), one to 5% of volatile, low molecular fatty acids, produced during the first step of the oxidation process, due to the splitting of the long aliphatic chain by the oxygen of the air; -(C2)nCH3, attached to the cyclopentane ring in position 3-, into two separate monocarboxylic acids. Nevertheless, this finely oxidized material has a much gentler odor of fatty acids, its viscosity is much lower, its color is straw-yellow, and its specific gravity is much higher. An additional steam distillation removes the low molecular fatty acids leaving analmost odorless product, which contains more than 80% of dicarboxylic naphthenic acids. In order to free them from. the non-saponifiable matter, an extraction with an alcohol-water mixture removes the acids, leaving insoluble the unsaponifiable matter. A subsequent distillation of the water-alcohol solution of the dicarboxylic naphthenic acids removes the solvent mixture, and the mixture of the dicarboxylic naphthenic acids can be finally fractionated under vacuum into narrow cuts of the individual homologs of the dicarboxylic naphthenic acids, which are believed to have formula as shown in (VIII) above. These acids are very valuable starting materials for purposes of further syntheses, in which aliphatic and aromatic dicarboxylic acids were previously being used, suchas for example, maleic, sebacic, succinic and adipic acids in the aliphatic series, and phthalic, and terephthalic acids in the aromatic series. Consequently, for the first time through my new two-step oxidation process a new class of dicarboxylic naphthenic acids is created, which lends itself to the manufacture of industrially valuable esters, salts, polyesters, polyamides, polyurethanes etc.,. from which different synthetic fibers, plastics, and elastomers can be cheaply produced.

The following examples are illustrative of this invention:

EXAMPLE 1 As the starting commercial oil, a semi-refined white oil, called AI-1C Process Oil, made by Socony Vacuum Co., was selected. Its physical-chemical properties were as follows:

Hot-acid testb1ack; n 1.4.808; di -0.886; dist. range C./10 mm. of to 95%173 to 223; flash point-15.85 C.; viscosity in centistokes/ZO C.3l; aniline pointplus 811 C. This oil, was exhaustively refined with a 20% oleum to a white oil, which had the following physico-chemical properties:

I-Iot-acid test-water-white; 11 1.407; d4 -0.869; dist. range C./'1O mm. of 5 to 95'%-l76 to 246; flash point-448 Cl; viscosity in centistokes/20 C.24.4; aniline pointplus 91? Cl; molecular weight292; Pour point-less than minus 50 C.; percent aliphatic side chains49; percent naphthenic rings-51.

100 pounds of above. white mineral oil were exhaustively oxidized at a temperature below 160 C., in the presence of a catalyst belonging to the class of fatty'acid salts of polyvalent heavy metals. conducted in a stainless steel autoclave, equipped with a turbomixer, and having a total capacity of 60 gallons. The pressure. during the air oxidation was kept below atmospheres. Every hour a. sample of the oxidized oil was withdrawn from the autoclave and analysed for the carbonyl number by the method of Bertram, described in the Journal Inst. of Petr. Techn, 34, 930 (1948-): The air oxidation was considered as finished as .soon, as in an hour interval the. carbonyl number did not" increase by more than one unit. Further oxidation. would be useless, because instead of increasing the content of the carbonyl-naphthenic acids, a considerable resinification would take place. The oxidation was considered as finished after a total oxidation time of hours. From 100 pounds of the starting white oil, 101 pounds of the oxidized product were obtained. Analysis of this product;

Colorr dark brown; appearancertwo separate. layers; odQra- -sharp-stingy of burned oil; d,4?-0.99.5.;. n 1.4.7.893, visc; in centistokes/ C.-8961; dist. range/ 1-0.

This oxidation was mrn.5%/131 C., 75%/256 C.; carbonyl No. 98; unsaponf'. matter20%; naphthenic and hydroxynaphthenic acids5l%; carbonyl-naphthenic acids37%; volatile fatty acids--2%.

This two-phase mixture without separating is subsequently oxidized in the same autoclave with a 35% aqueous solution of potassium permanganate as follows:

The 101 pounds of the product are saponified and further oxidized with about 120 pounds of a 35% aqueous solution of potassium permanganate. This amount was calculated from the quantitative analysis by using an excess of one mole of the IMn04 for the carbonyl group in each mole of the carbonyl-naphthenic acids; in excess of two moles of KMnOi for the methoxy-group in each mole of the hydroxy-naphthenic acids, and in excess of three moles of KMnOa for the methyl group in each mole of the naphthenic acids.

First the 101 pounds of the air oxidized oil were heated to a temperature of about 70 C. At this temperature, while thoroughly stirring, at atmospheric pressure, the calculated amount of the above mentioned KMnO4- aqueous solution was slowly added and during the addition, the temperature was maintained at about 70 C. by the use of a cooling bath. After the exothermic reaction was completed the mixture was allowed to cool to room temperature, at which temperature it was maintained while continuously stirring for about 24 hours. Every hour a sample of the oxidized product was withdrawn and its saponification number was determined. The reaction was considered as finished when in an hour interval no significant increase in the saponification number Occurred. Afterwards, the mixture was separated into two layers. The lower, aqueous layer was used for the regeneration of the KM1'104, and the upper, light colored oily layer, was washed thoroughly with hot water, and by steam distillation freed from the volatile low molecular fatty acids. The remaining oil was dried at 100 C., under vacuum and finally filtered. The obtained amount of the final product, which is believed to be predominantly a mixture of homologs of dicarboxylic naphthenic acids (VIII), was analysed and had the following physicochemical properties:

Color-straw yellow; odoracidic; viscosity in centistokes/20 C.-l; unsaponifiable matter23%; saponifiable matter77%; acid No. 386; saponif No. 391. The product gives typical reaction of dicarboxylic acids.

This mixture of homologs of dicarboxylic naphthenic acids can be easily esterified with polyalcohols, as for example with glycerine, yielding resinous polyesters. However, in some cases, where a more pure polyester is desired, the unsaponifiable matter must be removed. The most economic way to do it is by theextraction of the dicarboxylic naphthenic acids with an aqueous solution of ethyl alcohol, in which the unsaponifiable matter is insoluble. The unsaponifiable matter, which consists, mainly of unreacted white oil and some naphthenic alcohols, is returned into the air oxidation process.

EXAMPLE 2 As the starting commercial white mineral oil, a product called Carnation White Oil, and made by L. Sonneborn and Sons Inc., was selected. Its physico-chemical properties were as follows:

Hot-acid test-water white; n 1.4587; d4 0.839; dist. range C./10' mm. of 5% to was 210 to 225; flash point-185 C.; viscosity in centistokes/20 C.-25; molecular weight-325; pour point-plus 28 C.; anili'ne point-plus 105 C.; percent aliphatic side chains- 23; percent naphthenic rings7-2.

pounds of this white mineral oil were oxidized with air under the same conditions as described in Example. l. After 14 hours of oxidizing, a product was obtained with the following physico-chemical properties:

Color-dark brown; appearance-two-separate layers;-

5 7 1.4917; viscosity in centistokes/20 C.-l200; dist. range/20 mm.-5%/6 2 C., 50%/225 C.; 75%/280 C.; aniline pointplus 60 C.; acid No. 172; saponif. N0. 265; carbonyl No. 128; naphthenic and hydroxynaphthenic acids-31%; carbonyl-naphthenic acids-51%; volatile fatty acids5%; unsaponif. matter-13%; recovery-l07 This dark colored, malodorous viscous liquid was oxidized in the same autoclave with a strong 50% aqueous solution of hydrogen peroxide as follows:

For 107 pounds of the air oxidized product about 100 pounds of the 50% hydrogen peroxide solution was used. This amount was calculated in the same way as indicated in Example 1. First the 107 pounds of the air oxidized white oil was heated to a temperature of about plus 50 C. At this temperature, while stirring,

. at atmospheric pressure, the calculated amount of 100 pounds of the 50% hydrogen peroxide solution was slowly added, and throughout the addition, the temperature was maintained at about plus 50 C. by the use of a cooling bath. After the exothermic reaction was completed, the mixture was allowed to cool off to room temperature, at which temperature it was maintained, while stirring thoroughly for about 20 hours. The oxidation reaction was considered as completed when after one more hour the saponification number of the oxidized product remained almost unchanged. Afterwards, the mixture was separated into two layers. The aqueous layer was discharged and the resulting light colored oily layer was washed with small amounts of warm water and the light volatile low molecular fatty acids removed by a steam distillation. The remaining oil was dried at 100 C.- under vacuum and finally filtered.

Analysis of this product: Recovery--115 pounds, 100 lbs. white oil.

Colorstraw yellow; odor--acidic; viscosity in centistokes/20 C.180; unsaponifiable matter--15%; saponifiable matter85%; carbonyl No. acid No. 370; saponif. No. 372. Gives typical reactions of dicarboxylic acids.

In order to remove the unsaponifiable matter, the oil is reacted with an aqueous solution of caustic soda, and the unsaponifiable matter is extracted from the resulting sodium salts of the dicarboxylic acids with benzene. By acidification with an inorganic acid the pure dicarboxylic naphthenic acids are obtained. By a subsequent vacuum distillation pure individual acids result.

EXAMPLE 3 As the starting commercial white mineral oil, a product called Superla No. 10a made by Standard Oil Co. of Indiana was selected. Its physico-chemical properties were as follows:

Hot acid testwater white; n l.464l; d4 0.85l; distil. range C./10 mm. of 5% to 95%-2l6 to 299; flash point184 C.; viscosity in centistokes/ZO" C.- 41; molecular weight345; pour point-plus 25 C.; aniline point-plus 106 C.; percent aliphatic side chains-44; percent naphthenic rings56.

100 pounds of this white mineral oil was oxidized with air under the same conditions as described in Example 1. After 13 hours of oxidizing, a product was obtained with the following physico-chemical properties:

Color-dark brown; appearancetwo separate layers; odorsharp and stingy as of burned oil; d4 1.004; n 1.485; viscosity in centistokes/20 C.l200; distil. range/l0 mm.--5%/l45 C., 50%/238 C., 75%/292 C.; aniline pointplus 59 C.; acid No. 137; saponif. No. 256; carbonyl No. 138; unsaponif. matterl8%; naphthenic and hydroxy-naphthenic acids-39%; carbonyl-naphthenic acids-46%; volatile low molecular acids5%; recoveryl0l pounds.

This dark colored, malodorous, viscous liquid was oxidized in the same autoclave with a 45% aqueous solution of ammonium persulphate as follows.

For the recovered 101 pounds of the air oxidized product, about 250 pounds of the 45% aqueous ammonium persulphate solution was used. This amount was calculated in the same way as indicated in Example 1. First the 101 pounds of the air oxidized white oil was heated to a temperature of about 60 C. At this temperature, while stirring thoroughly, under atmospheric pressure, the calculated amount of 250 pounds of the 45 ammonium persulphate solution was slowly added and through the addition the temperature was maintained at about 55-60 C. by the use of a cooling bath. After the exothermic reaction was completed, the mixture was allowed to cool off to room temperature, at which temperature it was held while stirring thoroughly for about 26 hours. The oxidation reaction was considered as completed, when after one hour more, the saponification number of the oxidized product remained practically unchanged. Afterwards, the mixture was separated from the aqueous layer, which was discharged. The strawyellow colored oily upper layer, was washed with small amounts of a warm saturated aqueous solution of sodium chloride and subsequently freed from the volatile, low molecular fatty acids by a short distillation with superheated steam.

Further purification of the obtained dicarboxylic naphthenic acids, if necessary, is performed as described in Example 1 or 2.

Essentially, the two-step oxidation process under the present invention can be applied to any commercial white mineral oil, or any mineral oil, from which previously through exhaustive refining all aromatic and unsaturated compounds have been removed. Also it is important that the white mineral oil does not contain parafiin waxes. Parafiin waxes when oxidized with air, yield fattyand hydroxy-fatty acids, which by further oxidation with aqueous peroxide solutions do not give the desired dicarboxylic naphthenic acids, as required under this invention, but give dark resinous and useless products. Therefore the success of this invention depends upon the proper selection of the white mineral oil, free from paraffin waxes and unsaturated and aromatic hydrocarbons. It is also proper to mention in this place, that by air oxidation alone from white mineral oils, dicarboxylic naphthenic acids cannot be obtained under any circumstances. I have found in my experiments that as soon as the maximum amount of the unsaponifiable matter is oxidized to monocarboxylic acids and their esters, as exemplified by Formulas II to VII, further air oxidation produces only resin-like dark useless products and not the desired light colored dicarboxylic naphthenic acids. Therefore the only way to arrive at such dicarboxylic naphthenic acids, is to interrupt the air oxidation process at the moment when no further conversion of unsaponifiable matter into carbonyl-naphthenic takes place and proceed with the oxidation using an aqueous solution of peroxide salts, which alone have the property to oxidize the carbonyl-, the methoxy-, and one of the methyl group into a second carboxyl group.

As is also evidenced in the specification and examples, the process of this invention is such that the desired dicarboxylic naphthenic acids can be produced economically, safely and efficiently, thus opening for the first time a new abundant source of this industrially im portant class of dicarboxylic acids.

It should be furthermore understood that the present invention is not based upon or dependent upon the theories which I have expressed, nor is the invention to be regarded as limited to the express procedure or material set forth, these details being given only by way of illustration and to aid in clarification of this invention.

Finally it shall be understood that I do not claim the process of air oxidation of white mineral oils into monocarboxylic acids as such.

What I claim is:

l. A two-step oxidation process for the manufacture of predominantly dicarboxylic naphthenic acids from white. mineral oils, which comprises, as the first: step, oxidizing said oils with airat temperatures. from 100 tov 200 C., under'pressure. not higher than 10 atmospheres, in the presence of a catalyst belonging to the class of polyvalent heavy metal salts of fatty acids, whereby the oxidation isv conducted until no appreciable increase in the; carbonyl number of the oxidized. oil occurs; said oxidation product being subjected to a second oxidation step, which comprises further oxidation with an aqueous solution of at peroxide salt, this final oxidation being conducted. until noappreciable increase in. the saponification number of the oxidized product occurs.

2,,A twostep oxidation process for the manufacture of. predominantly dicarboxylic naphthenic acids from white mineral oils, which comprises, as the first step, oxidizing said oils with air at temperatures from 100 to 209" C.,. under, pressure not higher than 10 atmospheres, inthe presence of a catalyst belonging tothe class of polyvalent heavy metal salts of fatty acids, whereby the oxidation is conducted. until no appreciable increase in the carbonylnumber of. the oxidized oil occurs; said oxidation product. being subjected to. a second oxidation step, which comprises further oxidation with an aqueous solution of aperoxide-salt, at a temperature not higher than 100 C., said peroxide salt being, present in a ratio of at least one mole for the carbonyl group in each mole of the carbonylnaphthenic acids, at least two moles for the methoxygroup in each mole of the hydroxy-naphthenic acids, and at least. three moles for one methyl group in the pentane ring of; each; mole of. the naphthenic acids, said final oxidation being conducted until no appreciable increase in the saponification number of the oxidized product occurs.

3;. A two-step oxidation process for the manufacture of predominantly dicarboxylic naphthenic acids from white mineral oils, which comprises, as the first step, oxidizing said oils with air at temperatures from 100 to 20.0: C., under pressure, not higher than 1Qv atmospheres, in the. presence of a catalyst belonging to the class. of polyvalent heavy metal salts of fatty acids, whereby the. oxidation. is conducted until. no. appreciable increasein the carbonyl number of the. oxidized oil, occurs; said oxidation product. being subjected to a second oxidation step, which comprises further oxidation with an aqueous. solution of a peroxide salt, at temperatures. not higher than 1.00" C.,, said. peroxide salt. being hydrogenperoxide, said hydrogen peroxide being present in a ratio of at least one mole for the carbonyl group in each mole of the carbonylnaphthenic acids, atv least two moles for the. methoxygroup in each moleof the hydroxy-naphthenic acids, at least three moles for one methyl group in the cyclopentane ring of each mole of the naphthenic acids, saidoxidation being conducted. until no appreciable increase in the saponification number of. the oxidized product occurs; said oxidized product being free from the low molecular volatile fatty acids by steam distillation and. after. Wash.

. ing and drying being further purified. from unsaponifiable matter by selective extraction of the saponifiable matter. with an aqueous solution of ethyl alcohol, and finally by fractionating vacuum distillation being divided into narrow fractions, each containing predominantly an individual dicarboxylic naphthenic acid.

References Cited in the file of'this patent UNITED. STATES. PATENTS James July 23, 1929 Denton Aug. 15, 1950 OTHER REFERENCES.

3 87 and 102.

Beilstein, vol- IX, page. 768. Beilstein, vol. IX, 2nd Supplement, p. 534. 

1. A TWO-STEP OXIDATION PROCESS FOR THE MANUFACTURE OF PREDOMINANTLY DICARBOXYLIC NAPHTHENIC ACIDS FROM WHITE MINERAL OILS, WHICH COMPRISES, AS THE FIRST STEP, OXIDIZING SAID OILS WITH AIR AT TEMPERATURES FROM 100* TO 200* C., UNDER PRESSURE NOT HIGHER THAN 10 ATMOSPHERES, IN THE PRESENCE OF A CATALYST BELONGING TO THE CLASS OF POLYVALENT HEAVY METAL SALTS OF FATTY ACIDS, WHEREBY THE OXIDATION IS CONDUCTED UNTIL NO APPRECIABLE INCREASE IN THE CABONYL NUMBER OF THE OXIDIZED OIL OCCURS; SAID OXIDATION PRODUCT BEING SUBJECTED TO A SECOND OXIDATION STEP, WHICH COMPRISES FURTHER OXIDATION WITH AN AQUEOUS SOLUTION OF A PEROXIDE SALT, THIS FINAL OXIDATION BEING CONDUCTED UNTIL NO APPRECIABLE INCREASE IN THE SAPONIFICATION NUMBER OF THE OXIDIZED PRODUCT OCCURS. 